1. Field of the Invention
The present invention relates to an end fence, a sheet feeding cassette, a sheet feeding device, and an image forming apparatus including the end fence.
2. Background of the Art
For example, as illustrated in FIG. 1A, a background sheet feeding cassette for use in an image forming apparatus, such as, a copying machine, a printer, a facsimile machine, and other similar image forming apparatuses, that includes a sheet feeding cassette main body 101 (hereinafter referred to as a “cassette main body 101”), a bottom plate 103, an end fence 104, and a sheet leading edge regulating part 105. The bottom plate 103 is rotatable up and down about a supporting point 102. The end fence 104 is slidable and can be fixed at any desired position. The sheet leading edge regulating part 105 aligns leading edges of sheets (S) as recording media accommodated in the cassette main body 101 (i.e., loaded on the bottom plate 103) in a sheet-feeding direction (hereinafter referred to as a “sheet feeding direction”). The bottom plate 103 is biased by a biasing device (not shown), such as, a plate spring, such that the leading edge side in the sheet feeding direction of the sheets (S) loaded on the bottom plate 103 rotates upward. The end fence 104 is slidable in the sheet feeding direction.
When loading the sheets (S) into the cassette main body 101, the leading edges of the sheets (S) in the sheet feeding direction are brought into contact with the sheet leading edge regulating part 105. Subsequently, the end fence 104 is slid and brought into contact with the trailing edges of the sheets (S) in the sheet feeding direction. Thus, the sheets (S) are aligned along the sheet feeding direction in the cassette main body 101 by the sheet leading edge regulating part 105 and the end fence 104.
As the sheets (S) are fed by a sheet feeding roller 106 one by one, and as the number of sheets (S) decreases in the cassette main body 101, the bottom plate 103 rotates upward about the supporting point 102. With such an upward rotation of the bottom plate 103, the leading edge side of the sheets (S) loaded on the bottom plate 103 is raised, and an uppermost sheet of the stack of sheets (S) is kept in a position of contacting an outer peripheral surface of the sheet feeding roller 106.
However, as the bottom plate 103 rotates upward, a distance between the leading edges of the sheets (S) loaded on the bottom plate 103 and the sheet leading edge regulating part 105 gradually increases. As a result, as illustrated in FIG. 1B, the uppermost sheet of the sheets (S) fails to adequately contact the sheet feeding roller 6, thereby causing a sheet feeding failure.
To prevent a sheet feeding failure, as illustrated in FIGS. 2A through 2C, the use of an end fence 108, including a sheet pressing element 107 that presses the trailing edges in a sheet feeding direction of sheets (S) accommodated in the cassette main body 101 toward the sheet leading edge regulating part 105, has been proposed, for example, in published Japanese patent application No. 2000-95356.
The sheet pressing element 107 is configured to rotate about a supporting point 109 along the sheet feeding direction. Further, the sheet pressing element 107 is biased toward the sheet leading edge regulating part 105 by a biasing device (not shown) such as a spring. When the sheet pressing element 107 does not contact the sheets (S) and when the number of the sheets (S) loaded on the bottom plate 103 decreases, the sheet pressing element 107 protrudes forward in the sheet feeding direction as illustrated in FIGS. 2A and 2C.
When loading the sheets (S) into the cassette main body 101, including the end fence 108, the leading edges of the sheets (S) in the sheet feeding direction are brought into contact with the sheet leading edge regulating part 105. Subsequently, the sheet pressing element 107 is brought into contact with the trailing edges of the sheets (S) while sliding the end fence 108 forward in the sheet feeding direction. The end fence 108 is fixed at this position. At this time, as illustrated in FIG. 2B, the sheet pressing element 107 is rotated to a retracted position (i.e., a position where the sheet pressing element 107 does not protrude forward in the sheet feeding direction) against a bias force of the biasing device, thereby strongly abutting the sheet pressing element 107 against the trailing edges of the sheets (S).
As the sheets (S) are fed by the sheet feeding roller 106 one by one and the number of sheets (S) decreases in the cassette main body 101, the bottom plate 103 rotates upward about the supporting point 102 as illustrated in FIG. 2C. With such an upward rotation of the bottom plate 103, the leading edge of the sheets (S) loaded on the bottom plate 103 is raised. At the same time, the sheet pressing element 107, abutting against the trailing edges of the sheets (S), presses the sheets (S) forward in the sheet feeding direction by the bias force applied by the biasing device. Thus, even when the bottom plate 103 rotates upward about the supporting point 102 as the number of sheets (S) loaded on the bottom plate 103 decreases, a distance between the leading edges of the sheets (S) in the sheet feeding direction and the sheet leading edge regulating part 105 is kept constant, and a contact between the uppermost sheet of the sheets (S) and the sheet feeding roller 106 is adequately maintained. As a result, the sheets (S) can be stably fed by the sheet feeding roller 106.
However, the end fence 108 may be fixed at an inadequate position by an unexperienced operator or by loading the sheets (S) carelessly in the cassette. Specifically, as illustrated in FIG. 3A, when the sheet pressing element 107 is brought into contact with the trailing edges of the sheets (S) while sliding the end fence 108 forward in the sheet feeding direction, the end fence 108 stops sliding and is fixed at a position where the sheet pressing element 107 is rotated forward and brought into contact with the trailing edges of the sheets (S) by the biasing device.
In this condition, when the bottom plate 103 is rotated upward as the number of the sheets (S) loaded on the bottom plate 103 decreases, the sheet pressing element 107, which has been rotated to a protruded position forward in the sheet feeding direction, cannot press the sheets (S) loaded on the bottom plate 103 forward toward the sheet leading edge regulating part 105. As in the case of the background sheet feeding cassette of FIG. 1B, a distance between the leading edges of the sheets (S) loaded on the bottom plate 103 and the sheet leading edge regulating part 105 gradually increases as the bottom plate 103 is rotated upward. As a result, as illustrated in FIG. 3B, the uppermost sheets inadequately contact the sheet feeding roller 6, thereby causing a sheet feeding failure.
To avoid an occurrence of a sheet feeding failure, for example, a mark which indicates a fixing position of the end fence 108 corresponding to a size of the sheet (S) may be attached to the cassette main body 101. However, such a mark is not useful when the sheet (S) of an irregular size is used. Moreover, even if the sheet (S) of a standard size is used, the size of the sheet (S) may vary among the different sheet manufacturers. Thus, even if the end fence 108 is fixed at the marked position corresponding to the size of the sheet (S), a sheet feeding failure may still result.
Thus, it is desirable to provide an end fence that enables sheets to be fed stably even when a bottom plate loaded with a stack of sheets is rotated upward in a sheet feeding cassette, a sheet feeding device, or an image forming apparatus comprising a sheet feeding cassette or device having such an end fence.